1. Field of the Invention
The present invention relates generally to a structure of an internal combustion engine. More particularly, to a lubricating structure for a valve train including a camshaft or the like in an internal combustion engine.
2. Description of Background Art
One of the most commonly used conventional lubricating structures for a valve train such as a camshaft or the like in an internal combustion engine is constructed as follows. More specifically, lubricating oil pumped up from an oil strainer by an oil pump flows past an oil filter as the oil is fed from the oil pump through a lubricating oil inflow path. The lubricating oil is thereby fed to an oil gallery. The lubricating oil is then supplied through a lubricating oil supply path branching off the oil gallery. This lubricating oil supply path constitutes one of a greater system of lubricating oil supply path for supplying the lubricating oil to different parts of the internal combustion engine through the oil gallery. There is known another structure, in which the lubricating oil having flowed past the oil filter does not flow through the oil gallery. More specifically, the lubricating oil having flowed past the oil filter is directly supplied to the valve train including the camshaft or the like through a lubricating oil supply path branching off a point near a lubricating oil outlet of the oil filter. See, for example, Japanese Utility Model Publication No. Hei 6-18007, Pages 2 to 3 and FIG. 4.
The invention disclosed in Japanese Utility Model Publication No. Hei 6-18007, as shown in FIG. 13 of the drawings, relates to a lubricating structure in an internal combustion engine 0E. This lubricating structure includes an oil pump 0Pf disposed on a shaft end of a crankshaft 01 of the internal combustion engine 0E. The lubricating structure works as follows. More specifically, rotation of the oil pump 0Pf as a result of rotation of the crankshaft 01 draws the lubricating oil from the oil strainer. The lubricating oil, the pressure of which has been boosted in the oil pump 0Pf, is sent through a lubricating oil supply path 0F1 to an oil filter 012.
The lubricating oil fed to the oil filter 012 flows through, and is filtered by, the oil filter 012. There are provided lubricating oil supply paths 0F2 and 0F3 branching off a point near a lubricating oil outlet of the oil filter 012. The lubricating oil supply path 0F2, of these two lubricating oil supply paths 0F2 and 0F3, is oriented horizontally. Part of the aforementioned lubricating oil is supplied through this horizontally oriented lubricating oil supply path 0F2 to an oil gallery 0F4. The lubricating oil supply path 0F2 is disposed to extend to a position near a water jacket of a cylinder block. Accordingly, the lubricating oil that has been preferably cooled is supplied to the oil gallery 0F4 through the lubricating oil supply path 0F2.
The lubricating oil fed to the oil gallery 0F4 is further supplied from the oil gallery 0F4 to a bearing portion and the like of the crankshaft 01 via a plurality of branch supply paths 0F5. In addition, another part of the lubricating oil is directly supplied to the valve train such as the camshaft and the like through the lubricating oil supply path 0F3 that is not connected to the oil gallery 0F4 and is oriented substantially vertically.
Conventionally, the supply of the lubricating oil to the valve train in the internal combustion engine is commonly accomplished through the supply path branching off the oil gallery as described above. However, in the type of lubricating oil supply structure for the valve train such as that described above, the valve train is disposed at a level relatively higher than other lubricating oil supply portions. Moreover, the distance between the valve train and the oil gallery is greater than the distance between each of the other lubricating oil supply portions and the oil gallery. As a result, a phenomenon occurs wherein the pressure of the supplied oil drops during a low speed operation of the engine or the like. When this phenomenon occurs, a sufficient amount of lubricating oil is not secured for the valve train. Therefore, there is a need for positive and effective lubrication in the valve train.
The lubricating structure in the internal combustion engine as disclosed in Japanese Utility Model Publication No. Hei 6-18007 has at least one advantage. More specifically, the structure allows the lubricating oil that has flowed through the oil filter to be supplied directly to the valve train via a supply path branching off a point near the outlet of the lubricating oil of the oil filter. This supply path is not routed through the oil gallery. The structure therefore has an advantage in that the aforementioned phenomenon of the pressure drop of the supplied oil supplied to the valve train can be prevented.
The lubricating structure of the invention as disclosed in Japanese Utility Model Publication No. Hei 6-18007 does not, however, ensure a sufficient amount of supply of the lubricating oil in the valve train. Therefore, there is a need for a concrete structural feature for securing a positive amount of supply of the lubricating oil. Moreover, the object of the invention disclosed in Japanese Utility Model Publication No. Hei 6-18007 is to promote preferable cooling of the lubricating oil by disposing the lubricating oil supply path in an extended position near the water jacket. That is, the invention does not originally have a clear object of securing a sufficient amount of the lubricating oil to be supplied to the valve train. Further, no consideration is given to a structural feature of the lubricating structure in terms of securing a sufficient amount of the lubricating oil to be supplied to the valve train by preventing a drop in the supply pressure of the lubricating oil to the valve train. Therefore, there is room for structural improvements to be made on the lubricating structure of the invention from the viewpoint of securing a sufficient amount of supply of the lubricating oil by preventing a pressure drop in the supply of the lubricating oil to the valve train.